Production of neutral tones in photographic emulsions



tamed Apr. 4, 1944 PRODUCTION OF NEUTRAL 'I'ONES IN PHOTOGRAPHICEMULSIONS Burt H. Carroll and Cyril J. Stand, Rochester, N. Y.,assignors to Eastman Kodak Company, Rochester, N. Y., a corporation ofNew Jersey No Drawing.

8 Claims.

This invention relates to photographic emul- I sions and particularly toa method for the formation of neutral tones in such emulsions.

It is known that the developed image of finegrain emulsions is rarelyneutral in color, being generally a brownish or warm tone. For manymaterials this is considered objectionable and the use of compounds inthe developer or the emulsion to produce a neutral tone is old. Manymaterials, including thiohydantoin and alkylated thiohydantoins havebeen suggested for this purpose. These materials, however, are notalways effective to produce neutral tones in emulsions.

It is, therefore, the principal object of the present invention toprovide a novel method for the production-of neutral tones inphotographic Application September 23, 1941, Serial No. 411,976

emulsions. A further object is to' provide a method for the productionof neutral tones in line grain emulsions. A still further object is to Iprovide novel compounds for producing neutral tones in bromide orbromoiodide emulsions.

These objects are accomplished by i'ncorporating in the emulsion or in aphotographic developer an aryl substituted thiohydantoin. Thesecompounds are especially effective inthe case of bromide orbromoiodideemulsions whereas many of the previously used compounds areeffective only-with chloride emulsions.

The aryl substituted thiohydantoins used according to our invention maybe added to the developer or introduced into the emulsion before thedevelopment. The introduction of the material into the emulsion may becarried out by adding' it to the emulsion at any stage after theripening process. Since the compounds are capable of reacting withsilver salts to form silver sulfide, they should not be added to theemulsion before or during the ripening process. They may a be added tothe emulsion at any subsequent stage in its manufacture such as bymixing a solution of the, agent with the emulsion before coating.

The amount of arylated thiohydantoin to be added to the emulsion mayvary considerably depending upon the composition of the compound and ofthe emulsion and the degree to'which the tone is to be changed. Thecompound are preferably added to the finished emulsions in smallamounts. of the order of milligrams per liter of emulsion containing 40grams of silver bromide per liter.

Compounds suitable for use according to our invention include arylatedthiohydantoins such as 1-,B-diphenyl-Z-thiohydantoin.

Our invention may be illustrated by the follow ing example: V

A gelatin silver bromide emulsion was prepared in a normal manner, asdescribed in the literature, a non-ammonia type being used. The emulsionin which the example was obtained was a fine-grain, moderate contrastmaterial of low speed. The 1,3-diphenyl-2-thiohydantoin was effective inemulsions of the. type described above, containing somewhat higheriodide content than is frequently used in the preparation of fine grainmaterials.

It will be understood that the examples included herein are illustrativeonly and that other compounds falling within the scope of the appendedclaim may be used in our process.

gelatino silver bromide emulsions which comprises ripening the emulsionand adding to it a N-diphenyl-2-thiohydantoin.

5. The method for producing neutral tones in sion capable of producingneutral tones on gelatino-silver halide emulsions which comprisesdevelopment, containing a N-diphenyl-Z-thiohyripening-the emulsion andadding to it 1,3-didantoin added after ripening. phenyl-z-thiohydantoin.8. A ripened silver halide photographic emul- 6. The method forproducing neutral tones in a sion capable of producing neutral tones onde- 1 Belatino silver bromide emulsions which comvelopment containing1,3-diphenyl-2-tlliohyprises ripening the emulsion and adding to ithydantoin added after ripening.

1 ,3-diphenyl-2-thiohydantoin. BURT H. CARROLL. 7. A ripened silverhalide photographic emul- CYRIL J. STAUD.

